With a boiling point of 40.degree. C., 1,1,1,3,3-pentafluorobutane (known under the name F365 mfc) is a potential substitute for liquid chlorofluoroalkanes which are banned by the Montreal Protocol, most particularly fluorotrichloromethane (F11; b.p.=27.degree. C.) and trichlorotrifluoroethane (F113; b.p.=47.degree. C.).
Processes allowing F365 mfc to be prepared are few in number and generally involve the fluorination of a chloro precursor such as 2,2-difluoro-4,4,4-trichlorobutane, 2-bromo-2,4,4,4-tetrachlorobutane or 1,1,1,3,3-pentachlorobutane.
Henne et al. (J. Am. Chem. Soc. 67, p. 1194-1197 and 1197-1199, 1945) chlorinate 2,2-difluorobutane to obtain, with a selectivity of 52.5%, 2,2-difluoro-4,4,4-trichlorobutane (F362 jfc) which is then fluorinated to F365 mfc. McBee and Hausch (Ind. Eng. Chem. 39, p. 418-420, 1947) fluorinate F362 jfc with HF/HgO or with the mixture SbF.sub.3 /SbCl.sub.5, but the fluorination yields do not exceed 15%. All these processes are characterized by low yields, essentially due to the lack of selectivity of the chlorination reactions leading to the chloro precursor.
Another method for the preparation of F365 mfc, described by Tarrant et al. (J. Am. Chem. Soc. 80, p.1711-1713, 1958), consists of the radical addition of CCl.sub.3 Br to 2-chloropropene and fluorination with HF, in the absence of catalyst, of the 1:1 addition product (CCl.sub.3 CH.sub.2 CBrClCH.sub.3) obtained, in a yield of 34%. This method does not improve the overall yield since, in this case, a lack of selectivity is observed due to the formation of telomers promoted by the radical initiation with benzoyl peroxide.
Another chloro precursor of F365 mfc is 1,1,1,3,3-pentachlorobutane which, according to Friedlina et al. Izv Akad. Nauk SSSR (6), p. 1333-1336 (1980) and (8), p. 1903-5 (1979)!, may be obtained by telomerization of vinylidene chloride with 1,1,1-trichloroethane or that of 2-chloropropene with CCl.sub.4 in the presence of iron pentacarbonyl. In both cases, a mixture of three telomers is obtained and the selectivity towards 1,1,1,3,3-pentachlorobutane (1:1 addition product) is insufficient to be of any definite economic value.
The direct preparation of F365 mfc according to the method of Bloshchitsa et al. (Zhur. Org. Khim 24(7), p. 1558, 1988) by the action of hydrofluoric acid and sulphur tetrafluoride on diketene constitutes, in point of fact, the only method leading to F365 mfc with an acceptable yield (70%). Unfortunately, this process uses two relatively uncommon starting materials, diketene and sulphur tetrafluoride.
F365 mfc is also a by-product in the manufacture of 1,1-dichloro-1-fluoroethane (F141b), but the similarity of their boiling points (F141b : b.p.=32.degree. C.; F365 mfc : b.p.=40.degree. C.) and the existence of a minimum-boiling-point azeotropic mixture do not allow ready separation of the two products. A separation process, based on the principle of distillation in the presence of an excess of HF, is however described in patent EP 395,793.
Amine/cuprous salt complexes are known catalysts for the addition of polyhalo compounds to olefins (Kotora et al., J. of Molecular Catalysis 77, p. 51-61, 1992), but these authors show that the yield of 1:1 addition product may pass from 97% for vinyl chloride to 11% for 1,2-dichloroethylene.